Abstract: In response to the requirements for the safe and reliable operation of transformers in the construction of new power systems, this paper proposes a load capacity evaluation method based on multi-physics field simulation. Firstly, a fast simulation of the transformer temperature field is carried out based on equivalent thermal parameters. Then, under the constraints of hot-spot temperature, top-oil temperature, average relative thermal aging rate and load limit, an evaluation model for the normal periodic load capacity of transformers is established to determine their maximum operating capacity. The results show that the hot-spot temperature and temperature field distribution of the transformer are in good agreement with the measured results, and the calculation efficiency is high. The average relative thermal aging is the main factor restricting the transformer's normal periodic emergency load capacity. The load rate that the transformer can withstand decreases with the increase of ambient temperature.